Peanut is a crop requiring a large amount of calcium (Ca). In case of Ca deficiency, peanut will be tender with etiolated stem and leaves, and slow plant growth. Ca deficiency has greater effect on the reproductive organ, which is mainly reflected as flower abortion, pod atrophy, black germ in seed kernel, germination rate loss or low survival rate of seedlings. Ca can strengthen metabolism of nitrogen and carbohydrates, promote transport and distribution of protein and other nutrients to seed kernel, reduce hollow pod, and improve pod plumpness of peanut.
Peanut is a crop requiring a large amount of potassium (K). K can activate a variety of enzymes, promote photosynthesis and carbohydrate metabolism, accelerate transport and accumulation of substances, promote growth and development of peanut plants, and improve pod yield and kernel quality. K can still enhance the regulation effects of cells on external environmental conditions, improve the drought resistance and cold resistance of peanut, and enhance the lodging resistance of plant.
Since Ca and K ions compete for the absorption sites on plasma membrane, high concentration of Ca inhibits K absorption, and the amount of K absorbed by peanut plant is decreased with the increase of Ca concentration in the pegging region. Peanut needs less Ca before the pod-bearing stage, but needs much K in the early growth stage. In order to avoid competitive absorption of K and Ca in production, the most effective method includes basal application of potassium fertilizer, and top application of calcium fertilizer in the pegging stage. However, top application of calcium fertilizer is labor-consuming and time-consuming, and peanut mulched in a plastic film is not convenient for furrowing for top application.
CN103193546A discloses a special double film-coated inorganic fertilizer for peanut, where the weight ratio of raw materials in an inner layer is as follows: 5-8 parts of urea, 8-10 parts of ferrous sulfate, 20-25 parts of normal calcium superphosphate, and the coating film material includes 3 parts of gelatin, 3 parts of sulfur and 2 parts of sodium silicate; and the weight ratio of raw materials in an outer layer is as follows: 5-10 parts of urea, 15-20 parts of diammonium phosphate, 15-20 parts of potassium sulfate, 1-2 parts of zinc sulfate, and 5-10 parts of attapulgite clay powder. Once-through application of the double film-coated fertilizer can meet the nutrient requirements of peanut in different growth stages. Attapulgite clay powder is used as a fast dissolving fertilizer adhesive, is rich in trace elements, and enriches soil nutrients. With inorganic fertilizers commonly used in production as raw materials, the fertilizer does not pollute the environment or crops, is characterized by reasonable formula, balanced nutrients and better use effects, can significantly improve the fertilizer utilization rate, and improve the peanut yield and quality. However, its outer layer material is very easily decomposed, and has no controlled release effect.
Many sustained release and controlled release fertilizers in the prior art are special for some crops, and do not have so obvious effects on other crops. Therefore, specially developing a controlled release fertilizer suitable for fertilizer demands of peanut in different growth stages is a research direction.